1. Technical Field
The embodiments herein generally relate to electrical circuits, and, more particularly, to a compact and voltage stable automatic change over switch.
2. Description of the Related Art
Generally, in developing countries and more particularly in rural areas such as Bihar, and UP are common occurrence. Typically, people have their own power back-ups for generating power such as UPS, generators, etc. or either rent from a power supplier for running the appliances. However, one would not realise that when the mains power is back, there is still power being consumed from the generator, or either they have to manually turn off the supply from the generator. To overcome this, automatic change over switches are deployed in order to change the power supply from the mains to the generator or vice-versa.
FIG. 1 illustrates a traditional automatic change over switch 100 having a transformer unit 102, a rectifier with filter unit 104, a double pole relay switch 106, and a load 108. The transformer unit 102 is a step down transformer that receives an input of 230 volts alternating current (AC) from the mains. The transformer unit 102 step downs the voltage from the mains to a lower voltage. The output from the transformer unit 102 is 12 volts. This output (12V) is fed as an input to the rectifier with filter unit 104. The output voltage of the transformer unit 102 is constant with respect to the input voltage. For example, if the input decreases to 115 volts AC, the output also decreases to 6 volt and the coil of the double pole relay switch does not energise.
The rectifier with the filter unit 104 receives the 12 volts AC from the transformer unit 102 and converts to Direct Current (DC) voltage. The DC output voltage from the rectifier with filter unit 104 is fed to the double pole relay switch 106. The double pole relay switch 106 includes a coil. Typically, the double pole relay switch operates when some specified voltage is applied to its coil (not shown in FIG. 1). Simultaneously, an input from the mains and a generator are fed to the double pole relay switch 106.
Depending upon the automatic change over switch circuit 100, the double pole relay switch 106 selects any one of the input fed (e.g., the mains or the generator) and connects to the load. The main supply is selected and connected to the load if the coil is energized by the mains. Else, the supply from the generator is selected and connected to the load. Thus, the selection of the mains supply entirely depends on the mains voltage. If there is a voltage supply from the mains, then the double pole relay switch 106 will select the mains and connects to the load. Else, if there is no supply from the mains, the double pole relay switch 106 selects the generator and connects to the load. In other words, there is a voltage at the coil that will drive the double pole relay switch 106.
But, if the input voltage at the transformer increases more than 250 volts the coil voltage increase more than rated voltage of the coil and may damage the relay coil and the transformer winding coil due to high current. Thus, there is a limitation for applying the input voltage more than 250 volts. Hence, the stability of the traditional automatic change over switch 100 will vary with the input voltage. Thus, there may be a variation of voltage even when there is a high voltage and a small voltage supply from the mains.
The double pole relay switch 106 may not work if there is a less input voltage at the input terminal. Further, the double pole relay switch 106 may burn if there is more voltage leading to destroying the entire automatic change over switch. In fact, the traditional automatic change over switch 100 does not resist high and may not work at low voltages. The voltage is not stable and the cost is also high due use of the transformer, and the double pole switch. Accordingly, there remains a need for a compact automatic change over switch which will withstand large voltage ranges and operate even in low voltage.